The present invention relates to a new and improved construction of a chair support or frame structure.
In its more specific aspects, the present invention relates to a new and improved construction of a chair support or chair frame structure for a chair with a seat holder or support and a backrest holder or support. The seat holder or support is connected at least at its front end, where the seat user's legs will fit, with a supporting or support structure forming a part of a foot support or chair base structure and at its backrest end with the backrest holder or support by means of a swivel joint or pivot joint possessing a substantially horizontal axis of rotation. The backrest holder or support possesses an arm or arm structure extending in the direction or the front end of the chair support or chair frame structure. The arm or arm structure is pivoted at its end at the supporting or support structure by means of a further swivel joint or pivot joint possessing a substantially horizontal axis of rotation. Between the front end of the supporting or support structure and the end of the arm or arm structure, there is positioned a spring or resilient element exerting a force on the backrest holder or support. This spring or resilient element is blockable and freely movable by means of an operating or actuating mechanism operated by an adjusting lever.
Chair supports or frame structures for chairs constructed with a backwardly-inclinable backrest holder, are known from various prior art constructions. In the simplest known exemplary form, one end of both the seat holder and the backrest holder is swivelably or hingeably connected in spaced relationship at a supporting structure about a respective horizontal pivot axis or shaft, and the seat holder or part is connected at its other end with the backrest holder by means of a swivel or pivot joint. When the backrest holder is tilted backwards, the backrest holder tilts through a greater pivot or tilt angle than the seat holder or part, and for this purpose one of the swivel or pivot joints is additionally constructed as a sliding joint or one of the swivel or pivot joints is arranged at a bracket mounted at the seat holder.
For the operation of the chair support it is necessary that a spring element, usually a compression spring, be positioned at the supporting or support structure. A force is exerted by the spring element upon the backrest holder or support in opposition to the force exerted by the chair user against the backrest holder. This spring element can be, for example, constructed as a gas spring or as a spiral spring.
In order to increase the seating comfort, it is known to block the compression spring element in a certain position of the backrest holder or support, thereby fixing the position of the backrest holder or support. For this purpose, there is provided at the chair support an adjusting lever connected with an operating linkage or rod system with which the blocking of the spring element and thereby the backrest holder can be undertaken. However, the disadvantage of this prior art construction is that a further adjusting lever is needed to release the blocked spring element, thus requiring an additional expenditure in equipment and attendant increased costs.